<!DOCTYPE html>
<html lang="en">

<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Document</title>
  <style>
    #head {
      height: 200px;
      background: seagreen;
    }

    #content {
      height: 400px;
      background: darkolivegreen;
    }

    #foot {
      height: 200px;
      background: darkmagenta;
    }
  </style>
</head>

<body>
  <div id="head"></div>
  <div id="content">内容部分</div>
  <div id="foot"></div>
  <script src="./jquery-3.4.1.min.js"></script>
  <script>

    $("#head").load("./header.html", function () {
      // 加载完做什么
      $("#myhead").css("color", "red")
    })

    $("#foot").load("./footer.html", function () {
      // 加载完做什么
    })



  </script>
</body>

</html>